The present invention concerns a composite device, as well as its manufacturing method. It particularly concerns a method for a composite device equipped with a micromachine and a circuit element, with the thin metallic film at the circuit element being protected by a protective film during etching of the sacrifice layer during the formation of said micromachine.
Silicon micromachining techniques have been widely used in recent years; they are applied to acceleration sensors and angular velocity sensors, for example, in which microscopic sensor elements are formed on top of a silicon semiconductor substrate.
An acceleration sensor is illustrated by the number 100 in FIG. 3 as an example of such a silicon micromachine.
This acceleration sensor 100 has a box area 122, arms 1211 to 1214, and fixed parts 1201 to 1204 that are formed on top of a silicon substrate 103. The box area 122 is formed into a rectangular shape and the arms 1211 to 1214 are connected to its four corners at one end, with each of the arms 1211 to 1214 being connected to each of the fixed parts 1201 to 1204 at the other end.
The fixed parts 1201 to 1204 are secured over the silicon substrate 103; on the other hand, the box area 122 and the arms 1211 to 1214 are constructed so that they can freely move without making contact with the substrate 103. It is constructed so that the arms 1211 to 1214 are bent vertically using the fixed parts 1201 to 1204 as support points when the acceleration sensor 100 is subjected to an acceleration force in the vertical direction. Resulting movement between the parallel and flat capacitor plates, consisting of the box area 122 and the substrate 103 causes the capacitance to change.
The simplified manufacturing processes of such an acceleration sensor 100 are illustrated in FIGS. 4(a)-(l), which will be explained below.
With reference to FIGS. 4(a)-(e), two monocrystalline silicon substrates, onto which a silicon oxide film is formed on the surface, are first prepared; they are bonded together by a direct bonding method while their silicon oxide films closely adhere to each other, with one silicon wafer being formed. Successively, the surface at one side, which is opposite from the side onto which a monocrystalline silicon thermal oxide film is formed, is polished into a structural layer 104, and the monocrystalline silicon layer on the other side becomes a substrate 103. The silicon oxide film, which was used for direct bonding, remains between said substrate 103 and the structural layer 104 as a sacrificial layer 101 (FIG. 4(a)).
An oxide film 105 is formed onto the entire surface of such a silicon wafer structural layer 104((b) of the same FIG.), with an opening 107 being formed through patterning by etching a specific region ((c) of the same FIG.).
The surface of the silicon structural layer 104 is exposed in opening 107. The exposed structural layer 104, in is removed with anisotropic dry etching by an RIE method using the oxide film 105 as a mask; so that the structural layer is formed in the same pattern as that of the oxide film 105((d) of the same FIG.).
The sacrifice layer 101, which is exposed at the bottom the opening 107 at the completion of said patterning, and the oxide film 105, which was used for patterning the structural layer 104, are removed by performing wet etching ((e) of the same FIG.)
Subsequently, ion implantation and thermal diffusion are performed, with ohmic layers 113 and 114 being respectively formed in the substrate 103 and the structural layer 104 (FIG. 10(f)).
Next, a resist film 115 is formed onto the entire surface ((g)) of the same FIG.), windows are opened at specific sections above the ohmic layers 113 and 114, then the decomposition of chromium and platinum occurs, with thin chromium and platinum films 116, 117, and 118 being respectively formed over the resist film 115 and the ohmic layers 113 and 114((h) of the same FIG.).
When the resist film 115 is removed, the thin chromium and platinum film 116 formed over the resist film 115 is removed together with the resist film 115 (lift-off method). On the other hand, the thin chromium and platinum films 117 and 118 formed over the ohmic layers 113 and 114 are not removed but remain with metallic electrodes being respectively formed at the substrate 103 and the fixed part 1204((i) of the same FIG.).
Furthermore, the entire [wafer] is soaked in a hydrofluoric buffer (BHF), the side faces of the sacrifice layer 101 are exposed, and the sacrifice layer 101 is etched from its side faces. During this procedure, in a region where the size of the structural layer area is large or where the width is wide, a portion of the sacrificial layer 101 remains. Accordingly, the structural layer 104 in that part is fixed to the substrate 103 by the sacrificial layer 101, forming fixed parts 1201 to 1204.
On the other hand, the sacrificial layer 101 underneath the of the structural layer 104 in a part where the area is small, or where the width is narrow, is completely removed. Accordingly, a space 72 is formed in the middle of the substrate 103 when the structural layer at that part is connected to the structural layer 54 which makes up the fixed part; a movable part, which does not make contact with the substrate 103, is thus constructed. The arms 1211 to 1214 and the box area 122 are constructed from such movable parts.
In this manner, the box area 122 and the arms 1211 to 1214 are supported by the fixed parts 1201 to 1204 in a condition in which they do not make contact with the substrate 103, the arms 1211 to 1214 are bent by the weight of the box area 122 when an acceleration is added, and the distance between the substrate 103 and the box area 122 changes.
Accordingly, thin metallic wires are connected to the electrodes 117 and 118 by wire-bonding, the box area 122 and the substrate 103 are connected to an external measuring circuit, not shown in the FIG., and it becomes possible to detect the change in the capacity between the box area 122 and the substrate 103 and to calculate the size of the acceleration.
However, as described above, a lift-off method is used for the formation of the thin chromium and platinum film 116 in the existing technology, and the processes are complicated. Moreover, the electrodes 117 and 118 could not be formed from a thin aluminum film, which forms a thin film wiring within an integrated circuit, when said lift-off method was used, which was becoming an obstacle when forming circuit elements and a micromachine on top of the same substrate.
The aim of this invention, which was created to solve the aforementioned inconveniences in the prior art, is to offer a technique that allows for the formation of electrodes in a composite device without using a lift-off method.
In solving the aforementioned problems, an embodiment in the invention is a manufacturing method for a composite device, consisting of: a process in which a mask film that has been patterned is formed over a structural layer which is formed over a substrate through a sacrificial layer; a process in which the aforementioned sacrificial layer is exposed through etching the aforementioned structural layer using said mask film as a mask; and a process in which the sacrificial layer is removed through the aforementioned exposed part by side etching, and in which movable parts are formed in parts of the aforementioned structural layer where the sacrificial layer underneath the bottom face is completely removed and fixed parts are formed in parts where the sacrificial layer underneath the bottom face remains. The invention is also characterized by consisting of: a process in which electrical elements are formed within the structural layer, which constructs the aforementioned fixed parts, before the formation of the aforementioned mask film; a process in which a thin metallic film, which at least includes electrodes for an external connection, is formed over the aforementioned structural layer; and a process in which said thin metallic film is patterned.
In another embodiment, a protective film is formed on the surface of the aforementioned electrode after forming the aforementioned thin metallic film and before forming the aforementioned mask film so that the aforementioned electrode cannot be etched when etching the aforementioned sacrificial layer.
In another embodiment, a passivation film that has been patterned can be formed over the aforementioned protective film after forming the aforementioned protective film and before forming the aforementioned mask film.
In a further embodiment, the aforementioned protective film over the aforementioned electrode may be removed using the aforementioned passivation film that has been patterned as the mask.
In an embodiment, the metallic wiring that connects the aforementioned electrical elements to each other may be formed by the thin metallic film upon patterning the aforementioned thin metallic film.
In another embodiment, the aforementioned substrate is secured over the conductive substrate, and an electrical connection with the aforementioned conductive substrate may be obtained from the back face of the aforementioned substrate.
In an embodiment the aforementioned passivation film is made of a silicon nitride film.
In an embodiment, the mask film is formed over the structural layer which is formed over the substrate through the sacrificial layer, the structural layer is etched and the sacrificial layer is exposed while using that mask film as the mask, the sacrificial layer underneath the bottom face of the structural layer is removed through side etching through that exposed part, movable parts are formed in the structural layer in areas where the sacrificial layer underneath the bottom face is completely removed, and the with fixed parts being formed in areas where the sacrificial layer underneath the bottom face remains. Therefore, a micromachine can be constructed with movable parts and fixed parts. However, electrical elements are forms within the structural layer which forms the fixed parts. Before forming the mask film described above, a thin metallic film that at least includes the electrodes for an external connection is formed over the structural layer and a circuit can be constructed by patterning that thin metallic film. Therefore, a micromachine and a circuit can be formed within the same substrate without using a lift-off method.
In this way, the protective film is formed on the surface of the electrode after forming the thin metallic film and before forming the mask film so that the electrode cannot be etched when etching the sacrificial layer and the surface of the electrode for an external electrical connection cannot be roughened, forming an electrode of good quality.
Also, a passivation film that has been patterned is formed over the protective film after forming said protective film and before forming the mask film, improving the reliability of the composite device. As such a passivation film, one that cannot be etched when removing the sacrificial film is ideal; in that case, it is possible to remove the protective film using the passivation film that has been patterned as the mask.
Furthermore, if metallic wiring that connects the electrical elements to each other is formed from the thin metallic film when patterning said thin metallic film, a composite device can be manufactured in ordinary manufacturing processes for an integrated circuit besides patterning the structural layer and removing the sacrifice layer.
Also, if an electrical connection with the conductive substrate is obtained from the back surface of the substrate when securing the substrate to said conductive substrate, such as a lead frame, an electrical connection of a capacitor which is constructed from movable parts and the substrate can be obtained without the formation of electrodes on the surface of the substrate.
An easy as well as low-cost manufacturing process is attained if the structural layer and the substrate described above are constructed of silicon substrates, and if the sacrificial layer is constructed of a silicon oxide film. Also, an easy process can be obtained if the passivation mask is formed of a silicon nitride film.